Rigid, flexible and composite solid objects having cellulose containing rice hull particles and radiation induced polymer and method of making same

ABSTRACT

Discrete, cellulose containing, rice hull particles are impregnated with a monomer, usually a liquid, having a radiation activatable reaction group, molded under pressure to place the particles in substantially touching relation and form an article, and subjected to high-intensity ionizing radiation to polymerize the monomer and bind the particles into an object of stable shape. Additionally, the monomer may be selected to produce objects that are rigid and hard or flexible and resilient. A composite layered article is also disclosed.

I Unlted States Patent 1151 3,660,223

Casalina May 2, 1972 RIGID, FLEXIBLE AND COMPOSITE References CitedSOLID OBJECTS HAVING CELLULOSE UNITED STATES PATENTS CONTAINING RICEHULL PARTICLES 2,710,276 6/1955 Mottet et a1. ..161/268 AND RADIATIONINDUCED POLYMER 2,817,617 12/1957 Rogers ..161/162 AND METHOD OF MAKINGSAME 3,077,417 2/1963 Kenaga 204/159. 12 3,287,203 11/1966 Elmendorf...161/268 3,372,042 5/1968 Wright 106/3822 [72] Inventor; Samuel L.Casalina, 71 Paddon Road, 3,420,761 1/ 1969 Feibush ..204/ 159.12

Watsonville, Calif. 95076 Primary Examiner-John T. Goolkasian [22] Med:1968 Assistant Examiner-George W. Moxon, ll [21 Appl. No.: 762,173Attorney-Warren, Rubin, Burcker and Chickering Related US. ApplicationData [57] ABSTRACT Continuation-impart of 5611 P Discrete, cellulosecontaining, rice hull particles are im- 1968. pregnated with a monomer,usually a liquid, having a radiation activatable reaction group, moldedunder pressure to place 1 Cl the particles in substantially touchingrelation and form an ar- 20 15 2 0/ C, 26 ticle, and subjected tohigh-intensity ionizing radiation to [51] Int. Cl. ..B32b 5/16, B32b21/02 polymerize the monomer and bind the particles into an object Fieldof Search of stable shape. Additionally, the monomer may be selected toproduce objects that are rigid and hard or flexible and resilient. Acomposite layered article is also disclosed.

7 Claims, 3 Drawing Figures RIGID, FLEXIBLE AND COMPOSITE SOLID OBJECTSI-IAVING CELLULOSE CONTAINING RICE HULL PARTICLES AND RADIATION INDUCEDPOLYMER AND METHOD OF MAKING SAME This is a continuation-impartapplication based upon my earlier filed, pending application Ser. No.720,33 1 filed Apr. 10, 1968.

The present invention relates to the formation of solid, or-

v ganic composite articles from discrete particles, and moreparticularly relates to the formation of such articles by the use ofionizing radiation.

I have previously discovered that a solid cohesive object may be fonnedfrom a liquid monomer and discrete forestry particles such as sawdust,wood chips, bark and nut shells. Since these forestry particles,consisting principally of lignocellulose, represent a waste material inthe forestry industry which is not heretofore been efficiently used,this earlier discovery has been highly advantageous. In addition, theability to cast or mold the monomer and lignocellulose particle mixtureinto many shapes and configurations and about other articles has beenfound to be very beneficial. This process and the product formed therebyare fully described in my patent application, Ser. No. 642,768.

In addition, I have also previously discovered that sheets oflignocellulose such asfiberboard may be impregnated with selected typesof liquid monomers and irradiated to produce a flexible, composite sheethaving increased durability and strength. This process and the productproduced thereby are fully described and set forth in my patentapplication, Ser. No. 645,293.

Still further, for certain applications it has been found to beadvantageous to impregnate relatively large (as compared to wood chipsor sawdust) wooden pieces with a liquid monomer by means of highpressure. The impregnated pieces are then irradiated to produce anarticle having improved surface durability with the strength of thearticle being primarily derived from the inherent strength of the woodbefore treatment.

Notwithstanding the various advantages which have been found to accrueas a result of the use of the above described processes and products, itis an object of the present invention to provide a solid cohesive objectwhich is formed from an inexpensive particulate material and which hasimproved strength and durability.

It is another object of the present invention to provide a solidcohesive article which is formed from a particulated material andmonomer and which is flexible and resilient.

Still another object'of the present invention is to provide a solidarticle having the advantages of high strength and surface durabilityand in addition flexibility and resiliency.

Additional objects and advantages of the present invention will beapparent from the specification in conjunction with the drawings, inwhich:

FIG. 1 is a schematic representation of the steps of the method of thepresent invention according to one embodiment;

FIG. 2 is a schematic representation ofthe steps of the method of thepresent invention according to an alternate embodiment;

FIG. 3 is a perspective view of a layered article produced according tothe method set forth in FIG. 2.

I have recently discovered that a substantial increase in the strengthand durability of the article produced can be achieved if a mixture ofrice hulls and radiation-activatable monomer is employed instead of amixture of lignocellulose 7 (separated only by entrapped air or monomerfilm or .both). The addition of monomer can be either before or afterpressure molding, as represented in FIG. 1 by the arrows from Monomer"to both Rice Hulls" and Pressure Molding." After the forming operation,the mixture is subjected to ionizing radiation for a sufficient periodoftime so that the radiation dose is such as to eflect at least partialpolymerization of the monomer. As used throughout the specification andclaims, the terms rice hull particles" and rice hulls" shall means thosewaste materials which are typically separated from the rice kernelduring the de-hulling operation and include such particles as stems andleaf material.

Rice hulls are presently of little or no economic value and oftennecessitate substantial expense and inconvenience in their disposal. Theproduct and process of the present invention, therefore, afiords ahighly advantageous use of this heretofore waste material. The ricehulls may be mixed with the monomer directly as they come from thehulling equipment or they may be passed through a screen or series ofscreens of pre-determined mesh in order to select particle size.Moreover, the rice hull particles may also be taken from the hullingequipment and ground or pulverized into smaller particles and thenpassed through a screen for mixingwith the monomer. For purposes ofdecorative effect, ground n'ce hulls may be combined with whole ricehulls and mixed with the monomer for radiation polymerization.

In order to vary the physical characteristics of the article or productproduced, it has been found that selection of the monomer is veryimportant. If one kind of monomer is selected, the product produced hasa strength which can be as much as 2%times greater than the strength ofa similar article produced from lignocellulose particles. If anothermonomer is selected, the article produced, even though formed of aparticulate material, is highly flexible and resilient. Examples ofmonomers suitable for use in the process and product of the presentinvention are set forth in US. Pat. No. 3,077,417 to Kenaga, and thedescription of the several types of monomers therein given by structuralformulae are incorporated by reference. Among the monomers described, itis preferred to use the esters of acrylates, methacrylates andethacrylates represented by the structural chemical formula:

, wherein n is an integer from 0 to 2 and m is an integer from 1 to 4,both inclusive. Thus, the preferred monomers are methyl methacrylate,ethyl acrylate, propyl acrylate and butyl methacrylate and theirmixtures. These monomers are commercially available in a liquid andpowdered, partially polymerized form, and they haveradiation-activatable reaction groups which polymerize with thecellulose in the rice hull particles.

An advantageous catalyst which promotes the radiation polymerization ofthese monomers is carbon tetrachloride (CCL). The radiation doserequired for the process of the present invention is reduced whenbetween 5 and 30 percent of the weight of the combination of monomer andcatalyst is carbon tetrachloride.

While these monomers will produce a solid cohesive object when combinedwith cellulose containing, rice hull particles and irradiated inaccordance with the present invention, the selection of certainmonomers, as above set forth, results in a substantial difference in thephysical properties of the, end product. When methyl methacrylateis-used, a rigid product having high strength and surface durabilityresults. When ethyl acrylate is employed,'a flexible and resilient andyet highstrength product is produced. Thus, the monomers earlierdiscovered to be graitable to a pre-fonned lignocellulose sheet toproduce a flexible sheet have been found to be advantageously employedwith rice hull particles to produce an article which has the advantagesof being castable to almost any shape and yet is flexible and resilient.

As will be seen from the examples set forth herein, the article producedwhen methyl methacrylate and rice hulls are irradiated is essentiallyinflexible relative to the flexibility achievable when ethyl acrylate isemployed. Accordingly, it is possible to achieve variations in theflexibility and strength of the articles produced by using mixtures ofmethyl methacrylate and ethyl acrylate. In addition, it has beendiscovered that parboiling the rice hulls prior to mixture with amonomer such as ethyl acrylate will result in even greater flexibilityof the object produced. 7

Irradiation of the rice hull particle and monomer mixture can beefiected at ambient or moderately elevated temperature and ambient orelevated pressure. The radiation dosage will vary with such factors asthe radiation energy the specific monomer used, and the nature andquantity of the catalyst or .promoter, if any is present, within themonomer. The molding pressure is typically between 20 and 100 psi, andthe ratio of monomer to cellulose-containing, particles may be betweenabout 3.8 to l and about 0.05 to 1. It has been found to be preferableto use a monomer-cellulose ratio of between r0.l-l.0 to l. The cost ofmanufacturing articles in accordance with'the present invention isprimarily dictated by the cost of the monomer employed and the cost ofradiation. This is'true since the rice hulls themselves do notconstitute a substantial part of the product cost. Accordingly, it isimportant to be able to minimize the amount of monomer employed whilestill maintaining the desired strength or resiliency characteristic ofthe article produced. As will be seen in the examples, an increase inthe strength of the article of more than two times can be demonstratedover similar articles produced from lignocellulose particles when aratio of only 0.7 to l of monomer to rice hulls is employed.

As is true for the product and process set forth in my previousapplication, Ser. No. 642,768, I have found that radiation for theproduct and process of the present invention may consist of or includesignificant amounts of electro-magnetic radiation, preferably havingwave lengths between 0.01 and 14A. Alternatively or additionally,radiation suitable for the process and product of the present inventionmay consist of or include significant amounts of electrons havingenergies between about and 15 mev and beta rays having energies between0.5 and 15 mev. The radiation source may be radio nuclide or anelectronic device such as an X-ray tube. Radio nuclides such as cobalt60, iridium 192, and cesium 137 may be formed as a by-product of nuclearreactor operations. Alternatively, the element metal, such as cobalt 59,may be subjected to neutron bombardment to form radio active cobalt 60.

In the process and product of the present invention, the total absorbedradiation dose sufi'icient to effect at least partial polymerization ofmethyl methacrylate monomer and 9 percent CCl, with rice hulls has beenfound to be at least about 0.6 megarad of penetrating ionizingradiation. The unit of radiation megarad" represents the absorption of10 ergs of energy per gram of material irradiated, A radiation dosesufiicient to cause at least 65 percent polymerization of the monomer isreferred to through out this specification and claims as partialpolymerization. The phrase substantially complete polymerization shallmeans between about 90 to 100 percent polymerization An absorbed dose ofabout 1.0 megarad is required to achieve substantially completepolymerization when methyl methacrylate and about 9 percent CC! is used.The radiation intensity set forth in my previously referred toapplication, Ser. No. 642,768, are suitable for use in the presentinvention in order to achieve the increased strength and durability ofthe irradiated product once the absorbed dose is about about 1.0megarad. Depending upon the intensity, the period of exposure istypically about minutes to 4 hours, although longer and shorterexposures are feasible as radiation intensities vary.

monomers suitable for use in the process of the present inventionusually are subject to substantial evaporation. Accordingly, radiationover a long period of time may result in evaporation which causes voidsin the product, a change in the ratio of monomer to rice hull particlesor a deterioration in the surface smoothness or durability. Lastly,irradiation at high intensity, which results in a rapid polymerizationof the monomer with the rice hulls, may result in increased strength ofthe product by reason of a more complete polymerization and greaterstrength in the bonding between the polymer and the rice hulls.Therefore, when the dose rate is increased, the strength and uniformityof the product and process of the present invention is also increased.

Referring now to FIGS. 2 and 3 of the drawing, a method and a product ofthe present invention is set forth in which the advantages of highstrength and surface durability as well as resiliency are incorporatedinto a single product. It has been found that large pieces of solid woodcan be pressure impregnated with a monomer having aradiation-activatable reaction group and irradiated to produce anarticle having high surface strength and durability. One application inwhich such a product has found wide spread use is in inlaid or parquetflooring. A disadvantage of previous floor tiles, however, has been thatthe tile is often laid upon concrete, which results in a flooring havingvery little resiliency.

The product set forth in FIG. 3 overcomes some of the previousdifficulties encountered with such inlaid floor tiles by providing alayer of resilient material 7 on the lower side of the impregnated woodmember 9, which results in a layered composite tile having high surfacestrength and substantial resiliency. This polymerized layered articlecan be produced in a manner which is easily integrated with the methodfor production of articles from monomer and rice hulls, as will best beunderstood by reference to FIG. 2. First, the solid wooden layer 9undergoes pressure impregnation with a monomer, such as methylmethacrylate in order that the end product has a high surface hardness.Secondly, rich hulls and a monomer such as ethyl acrylate may be mixedand pressure molded as layer 7 on one side of the wood member 9. This ispreferably accomplished by placing the pressure impregnated woodenmember 9 at the bottom of a mold and packing the rice hull monomermixture on top thereof to the desired thicknes. The layered combinationis then exposed to ioniz ing radiation to cause polymerization of bothmonomers with respective cellulose bearing material and to cause a bondat the interface 11 between the wood and the particulated rice hullmixture. It is quite feasible to vary the order of some of the abovesteps. For example, wooden layer 9 may be pressure impregnated withmonomer while in the mold. Moreover, rice hulls may have the monomeradded while also in the mold (as indicated by the arrows). The samelevel of radiation intensity satisfactory for producing the flexible orrigid articles formed exclusively from particulated material will besatisfactory for the irradiation of the layered material.

It is also feasible to make the layered article by forming the entirefloor tile out of rice hull particles. This can be accomplished byforming layer 9 of a mixture of rice hulls and methyl methacrylate,which will produce a high strength product. On top of this layer, asecond layer 7 of rice hulls and ethyl acrylate can be placed. Therewill be some diffusion of the two monomers at interface 11 which willresult in a gradation of the flexibility from very flexible in layer 7to very hard in layer 9. Irradiation of the combination, however, willproduce a floor tile having a very hard surface 13 and yet a resilientbase layer 7. As will be understood, this approach can be used in otherapplications where it is desirable tohave a gradation between a rigidsurface and a resilient surface The improved physical characteristics ofthe product produced by the process of the present invention overprevious articles, and particularly the high strength and flexibilitywhich is achievable with the process of the present invention, may beclearly demonstrated by the following examples.

EXAMPLE I Small castings of fir (conifer) sawdust were prepared bygrinding the sawdust and passing it through a screen in order to screenout large particles. The'sawdust was pressed into 1 inch square by Ainch thick forms and a monomer solution consisting of 91 percent methylmethacrylate and 9 percent carbon tetrachloride was added. The moldswere sealed with a plastic bag and irradiated within a ring of cobalt 60rods having a total of 11,000 Curies of that radio nuclide for 3 hours.The dose rate was approximately 1 megarad per hour. In an exactlyanalogous fashion, rice hulls were ground and passed through the samescreen. They were placed in molds of the same size with the same monomercomposition added and irradiated by the same source for the same lengthof time.

The castings were tested by means of a Wabash hydraulic press having a4-inch ram by loading the cubes on their opposite l-inch square facesand applying force axially until fracture was observed. The results arethe number of pounds necessary to produce a complete single fracturing.

Small castings of fir (conifer) sawdust were prepared as set forth inExample I. The sawdust was, however, pressed into l5/l6-inch diametercylinders which were 1% inches in height. A 91 percent methylmethacrylate 9 percent carbon tetrachloride monomer mixture was used,and the sawdust irradiated by a 33,000 Curie source having aconfiguration which caused the dose rate to be about 6 megarads perhour. The cylinders were irradiated for 25 minutes. Rice hull particleswere ground, screened and pressed into a cylinder of the same size. Themonomer was the same, and the radiation conditions were also the same.The results of compression tests with the cylinders being loaded by ahydraulic press on their ends are set forth in Table 2. The numbers arethe pounds required to produce a complete fracturing. The reduction inthe total strength over the examples set forth in Table l is the resultof the difference in the physical configuration of the articles tested.The increase in strength of the rice hull particles over that of thesawdust is again, however, strikingly demonstrated. The ratio of monomerto sawdust and monomer to rice hulls was approximately 0.7 or 42 percentmonomer by weight.

Relatively thin sheets of the product of the present invention wereprepared by casting and irradiation. One set of sheets was formed from amixture of rice hulls and ethyl acrylate monomer having 9 percent byweight carbon tetrachloride. The ratio of monomer to rice hulls wasapproximately 0.25 to l or about 20 to 21 percent monomer. The sheetswere cast to have the following dimensions: 2 by 3 by V4 inch thick. Asecond set of sheets was cast having the same dimensions and usingmethyl methacrylate. A third of sheets was cast using parboiled ricehulls and ethyl acrylate. All sheets were irradiated by a 33,000 Curiesource having an approximate dose rate of 6 megarads per hour for 25minutes. The sheets were then clamped or secured along one of the 2 inchsides and a bending force applied at the opposite side approximately Zlinch away. Table 3 sets forth the force required, in grams, to bend ordisplace the sheets through As indicated in the table, the flexibilityof the sheet produced by ethyl acrylate is much greater than the sheetsproduced by methyl methacrylate. In addition, it will be seen that theuse of parboiled rice hulls results in a further increase inflexibility.

Rice hulls and a monomer solution comprised of 91 percent ethyl acrylateand 9 percent carbon tetrachloride were cast into a first set of stripsmeasuring 1% by 3 by 3/16 of an inch. The ratio of monomer to rice hullswas approximately 0.25 to l or 20 to 21 percent monomer. Similarly,sawdust and the same ethyl acrylate monomer were cast into strips of thesame size. All strips were irradiated by a 33,000 Curie source arrangedin a configuration providing a dose rate of approximately 6 megarads perhour for 25 minutes. The samples were then tested in tension untilfailure. The results are given in Table 4 as pounds required to causefailure. As will be seen from Table 4, the improved strength of the ricehulls, even when cast in flexible strips, over that of thelignocellulose composite strips is again demonstrated.

1. A solid cohesive object formed from particulate material and havingstability of shape comprising:

a. a multiplicity of discrete, cellulose containing, rice hull particlescompacted into substantially touching relation to act as structuralelements and formed to a predetermined shape of said object; and

b. a polymer disposed in and substantially filling the intersticesbetween said rice hull particles, said polymer being formed from amonomer having a radiation-activatable reaction group, said monomerbeing included in a ratio of at least 0.05 monomer to said rice hullparticles by weight and being radiation polymerized with the cellulosein said rice hull particles by ionizing radiation, and

said polymer cohesively binding said particles in the shape of saidobject.

2. An object as defined in claim 1 wherein the ratio of said monomer tosaid rice hull particles is in the range of between about 3.8 to l andabout 0.05 to l by weight.

3. An object as defined in claim 1 wherein the ratio of said monomer tosaid rice hull particles is in the range of between about 1.0 to l andabout 0.15 to l by weight.

4. An object as defined in claim 1 wherein said polymer is formed from aliquid monomer having the chemical structural fonnula where n is anintegerfiomfi to 2 and m is an integer from 1 to ticles are parboiled.

l I '0' l l UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo. 3, 660, 223 Dated May 2, 1972 Inventor(s) Samuel L. Casalina It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

' Column 1, line 43, "particulate" should read particulated-- Column 3,line 50, "element" should read elemental line 59, after "irradiated",change the comma to a period line 65, after "polymerization", insert aperiod line 72, "about about" should read above about Column 5, in Table2, line 70, after "Rice Hulls", cancel "11". Column 6, line 13, after"2172" change "inch" toread inches line 29, in Table 3, under columnheading "No. 3", far "Rice Hulls (Parboiled) insert 779 Signed andsealed this 2nd day of January 1973.

(SEAL) Attest:

EDWARD M.FLETCHERY,JR. ROBERT GOTTSCHALK I Attesting OfficerCommissioner of Patents :ORM po'wso (10459) USCOMM-DC wan-Pee U.S,GOVERNMENT PRINTING OFFICE: 19" 0-566'334,

2. An object as defined in claim 1 wherein the ratio of said monomer tosaid rice hull particles is in the range of between about 3.8 to 1 andabout 0.05 to 1 by weight.
 3. An object as defined in claim 1 whereinthe ratio of said monomer to said rice hull particles is in the range ofbetween about 1.0 to 1 and about 0.15 to 1 by weight.
 4. An object asdefined in claim 1 wherein said polymer is formed from a liquid monomerhaving the chemical structural formula where n is an integer from 0 to 2and m is an integer from 1 to 4, both inclusive.
 5. An object as definedin claim 4 wherein said monomer is methyl methacrylate.
 6. An object asdefined in claim 4 wherein said monomer is ethyl acrylate.
 7. An objectas defined in claim 6 wherein said rice hull particles are parboiled.